Synchronization in an Uplink Spatial Division Multiple Access Mode of a Wimax Wireless Communication System

1. A method for synchronization in an uplink spatial division multiple access mode of a WiMAX wireless communication system, the method comprising the steps of: allocating a mixed sequence of first and second tile patterns for uplink slots of a mobile station; detecting embedded pilot signals in mobile station data traffic; calculating a first pilot signal phase difference within the first tile pattern and a second pilot signal phase difference within the second tile pattern; estimating a time error and a frequency error of the pilot signals; sending information about at least one of the time and frequency error to the mobile station; and synchronizing the uplink transmit signals of the mobile station in response to at least one of the time error and frequency error, wherein the allocating step includes allocating a complementary sequence of tile patterns to two mobile stations.

2. The method of claim 1 wherein the calculating step includes averaging the pilot signal phase differences for the different tile patterns over all uplink slots for a mobile station.

3. The method of claim 2 wherein the estimating step includes multiplying a pre-determined constant matrix with the averaged pilot signal phase difference associated with a mobile station to obtain an estimated timing error and frequency error of the mobile station.

4. The method of claim 3 wherein the constant matrix is dependent on FFT size and symbol interval of the communication system.

5. The method of claim 1 wherein the synchronizing step include correcting timing and frequency error by data symbol rotation.

6. The method of claim 5 wherein the data symbol rotation is proportional to the estimated timing error and frequency error.

7. The method of claim 1 wherein in the calculating step the phase of the pilot on each corner of a tile is φ n , m ( t ) = 2 ⁢ π ⁡ ( τ N ⁢ n + mT s ⁢ Δ ⁢ ⁢ f ) + Φ t , ⁢ φ n + 3 , m ( t ) = 2 ⁢ π ⁡ ( τ N ⁢ ( n + 3 ) + mT s ⁢ Δ ⁢ ⁢ f ) + Φ t φ n , m + 2 ( t ) = 2 ⁢ π ⁡ ( τ N ⁢ n + ( m + 2 ) ⁢ T s ⁢ Δ ⁢ ⁢ f ) + Φ t and φ n + 3 , m + 2 ( t ) = 2 ⁢ π ⁡ ( τ N ⁢ ( n + 3 ) + ( m + 2 ) ⁢ T s ⁢ Δ ⁢ ⁢ f ) + Φ t where the tone index and OFDM symbol index of a tile are {n, n+1, n+2, n+3} and {m, m+1, m+2} respectively, t is tile index, N is Fast Fourier Transform size of the OFDMA system, T s is the OFDM symbol interval including cyclic prefix, and Φ t is a common phase associated with tile t.

8. The method of claim 7 wherein an average of pilot phase difference is calculated as θ _ A = φ _ n + 3 , m - φ _ n , m + 2 = 6 ⁢ π N ⁢ τ _ - 4 ⁢ π ⁢ ⁢ T s ⁢ Δ ⁢ ⁢ f _ .

9. The method of claim 7 wherein the average of pilot phase difference for the first pattern is φ _ n + 3 , m = 1 T A ⁢ ∑ t = 1 T A ⁢ ⁢ φ n + 3 , m ( t ) where T A represents number of first pattern tiles for the mobile station, and the average of pilot phase difference for the second pattern is θ _ B = φ _ n , m - φ _ n + 3 , m + 2 = - 6 ⁢ π N ⁢ τ _ - 4 ⁢ π ⁢ ⁢ T s ⁢ Δ ⁢ ⁢ f _ .

10. The method of claim 9 wherein the estimate of timing error and frequency error for the mobile station is [ τ _ Δ ⁢ ⁢ f ] = [ 6 ⁢ ⁢ π N - 4 ⁢ πT s - 6 ⁢ π N - 4 ⁢ π ⁢ ⁢ T s ] - 1 ⁡ [ θ _ A θ _ B ]

11. The method of claim 1 wherein the synchronization step applies a phase rotation to each data symbol according to ϕ n , m + 1 = - 2 ⁢ π ⁡ ( τ _ N ⁢ n + ( m + 1 ) ⁢ T s ⁢ Δ ⁢ ⁢ f _ ) where the data symbol is on tone n and OFDMA symbol m+1 of the tile.

12. A mobile station operable for synchronization in an uplink spatial division multiple access mode of a WiMAX wireless communication system, the mobile station comprising: a transmitter operable to send data traffic; a receiver operable to receive an allocation of a mixed sequence of first and second tile patterns for uplink slots transmissions and information about a time and/or frequency error from a base station that detects embedded pilot signals in the transmitted data traffic, calculates a first pilot signal phase difference within the first tile pattern and a second pilot signal phase difference within the second tile pattern, and estimates a time and/or frequency error of the pilot signals to be sent to the mobile station; and a processor coupled to the transmitter and receiver, the processor operable to synchronizing the uplink transmit signals of the mobile station in response to the time and/or frequency error information; wherein the allocation includes a complementary sequence of tile patterns allocated to two mobile stations.

13. A base station operable to provide synchronization in an uplink spatial division multiple access mode of a WiMAX wireless communication system, the base station comprising: a receiver operable to receive mobile station data traffic; a transmitter operable to send an allocation of a mixed sequence of first and second tile patterns for uplink slots transmissions to a mobile station, and send time and/or frequency error information to the mobile station for synchronization; and a processor coupled to the receiver and transmitter, the processor operable to determine the allocation of the mixed sequence of first and second tile patterns to be sent to the mobile station, detect embedded pilot signals in the transmitted data traffic from the mobile station, calculate a first pilot signal phase difference within the first tile pattern and a second pilot signal phase difference within the second tile pattern, and estimate a time error and a frequency error of the pilot signals to be transmitted to the mobile station; wherein the allocation includes a complementary sequence of tile patterns allocated to two mobile stations.